The photoreceptoral component of the electroretinogram (ERG) of the carp retina is isolated through the application of sodium aspartate and its adaptive and spectral properties studied. A second, slow potential, presumably of glial origin, is associated with receptoral activity. The sensitivity of the slow potential to potassium is being studied with ion- specific microelectrodes. A second effort deals with onset of function in developing amphibian photoreceptors. The effects of Vitamin A deprivation on intact eyes and others raised in a non-nutrient culture medium are assessed.